(1) Field of the Invention
This invention relates to a worm drive apparatus, and more particularly to metal working machines utilizing worm screw and worm rack mechanisms to provide precise component movement within those machines.
(2) Prior Art
Worm drive mechanisms have been used in gear units to move machinery components for many years. It is an effective method for transmitting rotary motion to linear motion. The axes of the worm gears and rack are however, spaced apart, and between them define a moment arm which may cause a slight non-linear arrangement in the worm, thereby creating extraneous forces, diminishing the efficiency that would otherwise be useful to move the components.
A typical worm and rack arrangement is shown in the machine tool art in U.S. Pat. No. 3,097,568 to Kampmeier, wherein a worm is disposed alongside and meshes with the teeth of a horizontal rack bolted to a ram. Rotation of the worm forces the rack and ram in a linear path.
This type of mechanism is also shown in U.S. Pat. No. 3,659,474 to Neugebauer, wherein a pair of worm gears are adapted to a single worm rack, the worm rack being attached to a table which is used to support a workpiece during its milling operation. The single worm rack on one side of the worm, as shown in the prior art, generates a radial component of force within the worm gear as a result of its thrust against a single rack. This radial component of force is a moment arm which causes deflection within the worm gear, and may cause undesirable loads on the machine carriage and its associated bearings. This bending force, in addition to the axial thrust through the worm created by the interaction of the worm gear shape on a single rack, effectuates the loading and deflection thereof and otherwise necessitates heavier components, bearings, motors and the like. The drive mechanism of the prior art also induces strain within itself, because slight deviations in the worm rack or worm gear are transmitted into their support systems which do not allow deflections therewith.
It is an object of the present invention to provide a worm drive mechanism that permits reduced component dimensions while still effecting the same work load.
It is a further object of the present invention to provide a worm drive mechanism which has a self-centering feature that eliminates the need for multibolting of the drive mechanism to the carriage.
It is yet a further object of the present invention to provide a worm drive mechanism which may be pivotably supported on its carriage, to facilitate its self-centering features.